Example of information from the Philadelphia FAR catalog. Screenshot from the document.

Pulling the data into a spreadsheet allows for some quick charts to show the relationship between building height and density.

It’s generally true that taller buildings are more dense, but not universally so. Buildings with the same density come in different shapes. Both the Liberty Place complex and the 230 South Broad St have an FAR of ~19.5; but Liberty Place includes a 960′ and 783′ tall towers. 230 South Broad St is just 250′ tall, but the building’s floorplates occupy 100% of the site.

By comparison, the densest zoning in DC is for 12 FAR (the C-5 zone), located in one of the few exception areas for DC’s height limit (allowing 160′ tall buildings along some blocks of Pennsylvania Ave NW). Quite a few blocks are zoned for up to 10 FAR, but nothing in DC can be built to an FAR of 15, 20 or 25, as in Philadelphia.

Considering DC’s effective downtown height limit of 110′ to 130′ combined with a maximum FAR of 10, it’s not hard to understand why DC has so many boxy buildings forced to occupy entire parcels. Likewise, DC’s height limit is indeed a hard limit on office density. Beyond 10 FAR, any additional density requires more height than the law currently allows.

In New York, the Empire State Building has a FAR of about 28. At less than half the height, the Equitable Building (inspiration for New York’s 1916 zoning code) has a FAR of 30.

Note: almost all of these very dense buildings are offices.

Back in Philadelphia, a more obvious example: the obvious relationship between building height and floor count (taller buildings have more floors).

This particular data set doesn’t include any buildings shorter than the City Hall tower; it’s not a complete record of all construction in Center City, just high rise buildings (the document was published in 2010). You can clearly see the approximate 500′ limit prior to 1987.

If you put all of these characteristics into one chart, you get something like this:

4 comments to Building Height and Density in Center City Philadelphia

Looking at the dot plot (height by density), you very much see the depression/ww2 lack of business investment.

I’d go one further an argue that the removal of regulations had led to greater inequality in buildings. If you have the resources to to build a 1000 foot tower that is great but you are sucking the oxygen out of the room.

Philadelphia, as casual user, does not seem to have a parking lot problem. Plenty of parking garages, but not many empty lots.

In terms of DC FAR, the biggest losers would seem to be government office buildings. Commerce, Labor are some of the worst offenders –not human sized. The RR building does work much better so it may have been a design problem. ATF building in NOMA is awful.

Richard like make the point that you can increase building heights and pay for Blue line. So go to a 20 FAR. How much can that actually generate?

Yes, there’s no doubt that the flip side of allowing more density is allowing more office space to be built in one fell swoop; the region will only have so much net new square footage to absorb at a time.

It’s true that Philly doesn’t have the same parking craters found in other places; I wonder if a lot of that is thanks to a lack of Center City urban renewal demolitions.

If DC were to dramatically allow more FAR, you’d face the same absorption issue – I don’t know that it would come close to paying for the Blue Line. It can be a key element of finance, but it won’t pay for much. That’s more an issue of structuring the payback, however. It will take time to realize that new density, the market would need to adjust, etc. The new density would be absolutely beneficial to transit use.

The report was written up before the zoning code overhaul in 2012 and references the old code, which I believe didn’t use FAR but blanket height controls; this explains a a high variation in FAR but relatively uniform height distribution among the mid-century buildings. In any case, most of the denser mixed-use skyscrapers >20 and residential highrises >12 FAR are still underzoned even after the rezoning. For example, the densest zone, CMX-5, was drafted using the Wanamaker Building as a model, which fits 1.3 million sq ft in 12 stories solely because of 100% lot coverage and a staggering 125,000 sq ft (1/2 block) parcel size. Neither of these factors are available for nearly any other Center City parcel. Most recent developments therefore have required substantial zoning variances or ad hoc acquisition of side parcels to fit the tower within the envelope.

That’s a good point about the difference of using FAR as a descriptive tool to measure the density of a building vs. as a regulatory one that essentially sets the maximum development capacity of a zone.